| 摘要 |
PURPOSE:To obtain a regulated reproducing output level without controlling a recording and reproducing power even at any track position by giving a negative slope on the film thickness of a recording layer along with a radius direction toward the outer periphery of a disc. CONSTITUTION:A recording layer 4 is formed so that the value of the film thickness of the layer has the negative slope along with the radius direction toward the outer periphery of a substrate 1, that is, it is formed to the thiner as approching to the outer peripheral direction. Thus, since the film thickness value of the recording layer 4 has the negative slope in the radius direction toward the outer periphery, its recording sensitivity characteristic is different according to its track position. Therefore, assuming that a disc medium is rotated at a regulated angular velocity and setting a recording laser power at a regulated level during that time, and assuming that each of the energy density of irradiating light in a track position (a') in the neighborhood of the outer periphery, a track position (b') in the near to intermediate part and a track position (c') in the neighborhood of an inner periphery is set as Ea'-Ec', bit diameters Da'-Dc' formed by the above are made almost equal. |
